1. Field of the Invention
The invention relates to sheet metal stamping operations and more particularly to an electromagnetic means for restraining the blank of sheet metal during a metal forming operation.
2. Description of the Prior Art
Sheet metal forming processes are typically employed in industries such as for example automotive, appliances, military, and electronics. The elimination of defects during the sheet metal forming process has been the subject of considerable study. The defects which typically occur during the forming process include thinning and tearing, plastic buckling or wrinkling, and elastic recovery or spring back upon unloading. Certain of these defects can be effectively minimized by controlling the blankholder or binder force and drawbead penetration which relate to the restraining forces applied to the sheet metal blank during a metal forming operation. By controlling and/or varying the blankholder force (BHF) during the sheet metal forming operation, certain defects can be eliminated and the formability of the product can be improved.
It has been found that by improved blankholder force application to the sheet metal blank being formed, better control of wrinkling and fracturing of the metal can be achieved. Also, it has been found that improved thickness profiles and reduced springback are effected. However, the conventional stamping presses, either mechanical or hydraulic, are generally equipped with nitrogen gas springs or hydraulic cushions as the means to exert the blankholder force, are seldom retrofitted to control the force due to the limited space available in the press and the complexity of the required hydraulic system.
It is an objective of the present invention to produce an electromagnetic blank restrainer which will overcome the shortcomings of the prior blank restraining systems.
Another objective of the invention is to produce an electromagnetic blank restrainer utilizing the benefits of variable blank holding forces created by the utilization of electromagnetic forces, either attraction or repulsion, to restrain the blank of sheet metal during a forming process of the sheet metal.
Still another objective of the invention is to produce an electromagnetic blank restrainer for applying variable forces created by a plurality of cooperating magnetic components to control the forces acting to restrain the blank of sheet metal during a stamping operation to form the blank into a stamped part.